LMTO band structure calculations

Fig. 8 a Valence band spectrum of Hf(Sio.5As0.5)As. b DOS curves obtained from LMTO band structure calculations on different ordered models for Hf(Sio.5Aso.5)As [119]. Reprinted with permission from [35], Copyright Elsevier... 

The starting Hamiltonian H has been also used to make a link between ab-initio LMTO band structure calculation and a DMFT treatment of correlations for the studies of LaTiOs [9] and Plutonium [10]. This last approach, assuming infinite dimension, goes beyond our approach. We only expect to be able to describe the coherent part of the spectrum, whereas the incoherent part leading to lower and upper Hubbard subbands are not accessible in our model, however as already stressed, variationally based. 

The near-IR spectra of crystalline samples of the two radical dimers [22]2 (R1 =Me, Et R2 = H) were measured <2005JA18159>. The absorptions in the mid-IR region between 650 and 3100 cm-1 are due to molecular vibrations of the dimer. A well-developed, low-lying absorption cutoff was interpreted as corresponding to a valence band to conduction band excitation. The optical energy gap values are qualitatively in agreement with the values predicted by the LMTO band structure calculations. 

Both, EH and LMTO calculations yield band structures with band overlap at the Fermi level meaning that a metallic conduction is expected. This is displayed in Fig. 3e and 3f. Indeed, Ca7Mg7j5Sii4 shows metallic conductivity. Thus, there are no localized spins but the HOMO states form a conduction band which, according to LMTO-band structure calculations, is exclusively due to x-orbital overlapping between adjacent ecliptically arranged Si 2 moieties along the stacking direction. 

The overall results of the LMTO band structure calculations are found to be the same as those obtained with the FLAPW method the shapes of their total energy curves are similar, aside from a 0.3 eV upward shift in the absolute energy for the LMTO cases. The equilibrium Wigner-Seitz radius is 3.37 a.u. in LMTO compared with 3.35a.u. in FLAPW and the bulk modulus is 0.57 Mbar (LMTO) compared with 0.56 Mbar (FLAPW). 

As is known in the case of binary systems, when their composition is close to equiatomic, d-ina-via metals form, as a rule, stable phases with Bl-type structures. But, as was observed by Vereshchagin and Kabalkina (1979) using a high-pressure treatment, it is possible to get B1 B2 (NaCl-CsCl)-type structural transitions with some oxides. The question of whether this could happen with d-met carbides was discussed by Ivanovsky et al (1988). These authors carried out LMTO band structure calculations for hypothetical TiC, VC and CrC compounds with a B2 structure. The lattice parameters were determined from the condition that the unit cell volumes of the CsCl- and NaCl-type phases were equal. In order to consider the influence of uniform isotropic compression the B2 VC calculations were carried out for crystal lattice volumes of 5 and 10% less than the equilibrium one. 

To probe the electronic structures of the materials in the solid state, band structure calculations on the crystal structure of compound 22 were carried out. The results obtained by using the linear muffin-tin orbital (LMTO) self-consistent field (SCF) method support the interpretation that compounds 22 (R1 = Me, Et R2 = H) are small-band-gap semiconductors. 

Earlier it was mentioned that the relativistic theory of electronic states in solids in many respects is identical to that of atoms. Since this is well described elsewhere, this section will only deal with some features of specific implementations of the theory in actual calculation methods used for solids, and the importance of relativistic effects — apart from those already discussed — will be illustrated by examples. Although Section 3 did refer to results of LMTO calculations, we did not describe how these included relativity. This section will deal with these items in the form of an overview, and the basic band structure calculations described relate to the density-functional theory [62,63]. Since magnetism is one of the most important solid state physics fields we shall discuss the simultaneous inclusion of spin-polarization and relativistic effects, in particular the spin-orbit coupling. In that context it appears that several of the materials where such effects are particularly large and interesting are those where electron... 

The first accurate band structure calculations with inclusion of relativistic effects were published in the mid-sixties. Loucks published [64-67] his relativistic generalization of Slaters Augmented Plane Wave (APW) method. [68] Neither the first APW, nor its relativistic version (RAPW), were linearized, and calculations used ad hoc potentials based on Slaters s Xa scheme, [69] and were thus not strictly consistent with the density-functional theory. Nevertheless (or, maybe therefore ) good descriptions of the bands, Fermi surfaces etc. of heavy-element solids like W and Au were obtained.[3,65,70,71] With this background it was a rather simple matter to include [4,31,32,72] relativistic effects in the linear methods [30] when they (LMTO, LAPW) appeared in 1975. 

This volume proposes to describe one particular method by which the self-consistent electronic-structure problem may be solved in a highly efficient manner. Although the technique under consideration, the Linear Muffin-Tin Orbital (LMTO) method, is quite general, we shall restrict ourselves to the case of crystalline solids. That is, it will be shown how one may perform self-consistent band-structure calculations for infinite crystals, and apply the results to estimate ground-state properties of real materials. 

The question of alternative structure can be answered by electronic-structure theory, and it turns out that a quantitative answer is slightly more complicated because different magnetic properties are calculated for the [NaCl] and [ZnS] types. Nonetheless, non-spin-polarized band-structure calculations are quite sufficient to supply us with a correct qualitative picture. This has been derived using the TB-LMTO-ASA method and the LDA functional, and they give the correct lattice parameters with lowest energies for both structure types [267], just as for the case of CaO. 

Figure 4 A crystal orbital Hamiltonian population (COHP) diagram for IrYellio, derived from LMTO-ASA band structure calculations...

After investigating the positron behavior, the next step is to solve the band structure and to calculate the momentum density p (p). It is rather controversial to describe the electronic structure of high-Tc superconductors by band structure. But it is almost the only way to obtain a calculated momentum density in order to interpret the positron measurements. We refer to the chapter by Pickett and Mazin in this volume (ch. 193) for a general discussion of band-structure calculations in superconducting cuprates. Studies in relation with positron annihilation have been made using different methods FLAPW (Massidda 1990, Massidda et al. 1991), LMTO (Bansil et al. 1988, Barbiellini et al. 1992,... 

An LDA band structure calculation is expected to yield a good description of the ground state properties of rather extended 4f-band Ce metal, provided it is carried out to self-consistency. Kmetko and Hill (1976) performed the first self-consistent APW band structure calculation for y- and a-Ce and pointed out the increase in hybridization of the 4f-states with the conduction band with reduction of the atomic volume. Glotzel (1978) reported the cohesive and magnetic properties of fee Ce obtained with the self-consistent relativistic LMTO method (Andersen 1975) and... 

The study of the band structure for (3-Ag2S (monoclinic structure at room temperature) and a-Ag2S (cubic structure above 453 K) is experimentally presented in [12] by using photoelectron spectroscopy and by using the FP-LMTO (full-potential linear muffin-tin orbital) calculation in theory. The band structure calculation was performed for a modified bcc structure, where silver atoms occupy two different positions 1) four silver... 

A half-metallic character has been proposed in another spinel oxide, LiCr204, by spin-polarised first principles density functional calculations (Figure 5.8). Both full potential linearised augmented plane-wave (FP-LAPW) and the LMTO methods were used to calculate the band structures. The lattice and other internal parameters for the cubic spinel structure were optimised with FP-LAPW calculations and subsequently the optimised parameters were used in the band structure calculations. Flowever, the experimental realisation of Li(Cr " " " )204 is still a challenge to confirm its predicted electronic and magnetic properties. 

---